Related papers: High-redshift quasars at $z \geq 3$: radio variabi…

Peaked-spectrum (PS) sources, known for their distinct peaked radio spectra, represent a type of radio-loud active galactic nuclei (AGN). Among these, megahertz-peaked spectrum (MPS) sources, which exhibit a spectral peak at a frequency of…

We present deep radio observations of the most distant complete quasar sample drawn from the Sloan Digital Sky Survey. Combining our new data with those from literature we obtain a sample which is ~100 per cent complete down to S_1.4GHz =…

Quasars at redshifts $z>6$ are an excellent probe of the formation and evolution of supermassive black holes in the early Universe. The population of radio-luminous quasars is of particular interest, as such quasars could potentially be…

We present optical identifications and redshifts for seventeen new high-redshift radio sources. Fifteen of these sources are radio galaxies; the remaining two are high-redshift, steep-spectrum, radio-loud quasars. These objects were…

We present an analysis of X-ray variability in a sample of 156 radio quiet quasars taken from the ROSAT archive, covering a redshift range 0.1 < z < 4.1. A maximum likelihood method is used to constrain the amplitude of variability in these…

We study the radio properties of moderately obscured quasars over a range of redshifts to understand the role of radio activity in accretion using the Jansky Very Large Array (JVLA) at 6.0GHz and 1.4GHz. Our z~2.5 sample consists of…

Gigahertz-Peaked spectrum (GPS) sources are compact active galactic nuclei, presumably young precursors of bright radio sources. The study of GPS radio properties provides information about the features of synchrotron radiation in…

Ultra-steep spectrum (USS) radio sources are good tracers of powerful radio galaxies at $z > 2$. Identification of even a single bright radio galaxy at $z > 6$ can be used to detect redshifted 21cm absorption due to neutral hydrogen in the…

We present millimeter and radio observations of 13 SDSS quasars at reshifts z~6. We observed eleven of them with the Max-Planck Millimeter Bolometer Array (MAMBO-2) at the IRAM 30m-telescope at 250 GHz and all of them with the Very Large…

We analyze the X-ray variability of 264 Sloan Digital Sky Survey spectroscopic quasars using the Chandra public archive. This data set consists of quasars with spectroscopic redshifts out to z~5 and covers rest-frame time scales up to Delta…

We present a milliarcsecond-resolution radio survey of 17 high-redshift (4 < z < 5.4) blazar candidates observed with the European Very Long Baseline Interferometry (VLBI) Network at 5 GHz. The primary objective of this study was to…

We present high resolution (subarcsecond) observations at 6.2 and 19.6 GHz made with the Karl G. Jansky Very Large Array of 113 radio-loud quasars that form a complete flux limited sample (> 70 mJy at 1.4 GHz), with spectroscopic redshifts…

We explore the radio properties of powerful (rest-frame luminosity $\gtrsim10^{28}$ W Hz$^{-1}$ at 500 MHz) high-redshift (z > 3.5) quasars. The aim of this study is to gain a better understanding of radio-loud sources at the epoch when…

This paper presents the first high-resolution and high-sensitivity study of the radio properties of optically selected type~2 quasars. We used the Very Large Array at 8.4 GHz to observe 59 sources drawn from the Sloan Digital Sky Survey…

We discuss flaring variability of radio emission of microquasars, measured in monitoring programs with the RATAN-600 radio telescope. We carried out a multi-frequency (1-30 GHz) daily monitoring of the radio flux variability of the…

We present a study of the radio and optical properties of the high-frequency peaker (HFP) blazar PKS 1614+051 at $z=3.21$ based on the data covering the time period of 1997-2024. The radio data are represented by the almost instantaneous…

We search for variable sources, using the data of the surveys conducted on the RATAN-600 radio telescope in 1980-1994 at 3.94 GHz. To test the radio sources of the RCR (RATAN Cold Refined) catalog for variability, we estimated the long-term…

We report about the multi-frequency (1-30 GHz) daily monitoring of the radio flux variability of the three microquasars: SS433, GRS1915+105 and Cyg X-3 during the period from September 2005 to May 2006. 1. We detected clear correlation of…

The redshift distribution of flat-spectrum radio sources with 5 GHz flux densities S>5 mJy is a key component in using current radio lens surveys to probe the cosmological model. We have constructed the first flat-spectrum radio sample in…

We present a three epoch survey for transient and variables in the extended Chandra Deep Field South at 5.5 GHz with the Australia Telescope Compact Array. A region covering $\sim$0.3 deg$^{2}$ was observed on timescales of 2.5 months and…